1. Field of the Invention
The present invention generally relates to a constant velocity universal joint for transmitting a constant rotational motion between two non-coaxial shafts. More specifically, this invention related to a tripod constant velocity universal joint providing improved efficiency through lower friction within the joint while simultaneously allowing for high articulation and plunge between the shafts.
2. Description of the Prior Art
Constant velocity ("CV") universal joints are well known in the art and are extensively used to translate rotational motion between a driving shaft and a non-coaxial driven shaft. They are primarily desirable for their ability to deliver a uniform output rotational speed which does not vary with rotation of the drive linkage or with articulation between the driving and driven shafts. A typical example of such an application is the drive linkage between the transmission and front wheels of a front wheel drive car. Such linkages are not only required to have non-coaxial shafts between the transmission and the wheel for transmitting the engine power, but must also allow for extensive articulation between the drive shaft and the wheel for purposes of steering.
The tripod constant velocity joint of interest for purposes of the present invention is a particular form of the constant velocity classification of universal joints. Tripod CV joints generally have an inner joint member housed within an annular outer joint member. Conventionally, the inner joint member has three radially extending trunnions equally spaced about the inner joint's axis of rotation. Upon each trunnion is journaled a roller assembly which engages a pair of parallel longitudinal guideways or tracks correspondingly provided upon the interior surface of the outer joint member. By example, U.S. Pat. No. 2,235,002 to Anderson shows a tripod CV joint in which the trunnions are cylindrical and the rollers are slidably mounted on the trunnions to allow for radial movement of the roller relative to the trunnion when necessitated by the inner joint member being angularly disposed in relation to the outer joint member.
Anderson typifies the early tripod CV joint in which the plane of rotation of the roller remains parallel to the inner joint member's axis of rotation. As a consequence of the typical operating conditions where the axes of the inner and outer joint members are non-coaxial, each roller's plane of rotation is at some angle to the longitudinal axis of its guideway. As the CV joint rotates, each trunnion of the inner joint member arcuately traverses a portion of the length of its respective guideway. The portion of the guideway traversed increases as the angle between the inner and outer joint members increases.
At any distance from the midpoint of a guideway's length, each roller's plane of rotation is at an angle to the longitudinal axis of the guideway equal to the angle between the inner and outer joints. Therefore, at any time each of the three rollers is also at a different angle, corresponding to a phase angle of the CV joint's rotation, with respect to its respective guideways. Because the plane of rotation of a roller does not remain parallel to the longitudinal axis of its guideways, the motion of each roller relative to its corresponding pair of guideways is a combination of rolling and sliding.
This sliding motion results in an increase in friction between the roller and the guideways whose intensity increases depending upon the phase angle of the assembly's rotation. This periodic increase in friction induces high fluctuations in the torque resistance of the inner joint member as seen at the driving shaft, and consequently produces a non-uniform output speed to the inner joint member. Loss of efficiency results along with a destructive wear effect upon the member of the CV joint.
To minimize this "periodic" sliding component of the roller motion, attempts such as that shown by Anderson included forming the guideways to match the path of the roller. Anderson also provides rollers which were slidably mounted on the trunnions to allow for radial movement of the roller relative to the trunnion. However, it can be readily recognized that the expense and durability of the composite guideway of the Anderson design has significant disadvantages in precision and cost. In addition, the periodic sliding motion of the roller is only reduced and not sufficiently eliminated so as to avoid the aforementioned sliding.
U.S. Pat. No. 4,192,154 to Nakamura et al illustrates another method for reducing the periodic sliding motion between the rollers and the guideways. Nakamura retains the use of a roller which is radially slidable upon the trunnion, but in addition provides a second roller member which rotatably circumscribes the spherical outer surface of the first roller member journaled on the trunnion. The spherical inner surface of the second roller member allows for a degree of articulation between the first and second roller members, while the second roller member's cylindrical outer surface allows for a rolling motion as the roller assembly traverses the guideways of the outer joint member.
However, the rolling action of the Nakamura design is limited to one side only of the second roller member. The opposing side is a sliding motion at twice the linear speed of the translational speed of the second roller member. This "asymmetrical" sliding motion reduces the efficiency of the Nakamura CV joint.
A second approach to limiting the sliding action between the roller member and guideways is disclosed in U.S. Pat. Nos. 4,828,534 and 4,490,126 to Orain. There a triplan CV joint is provided whose roller member consists of a plurality of needle rollers disposed between the trunnions of the inner joint member and the guideways of the outer joint member. In U.S. Pat. No. 4,828,534, cups are provided between the spherical trunnions and the needle rollers. The inner surface of the cup is spherically concave so as to mate with the exterior spherical surface of the trunnion, whereas the outer surface of the cup is planar to provide a flat surface upon which the needle rollers traverse.
In contrast to Nakamura, this design avoids the asymmetrical rolling-sliding action of opposing sides of the rollers. However, as has been the disadvantage before, the periodic sliding motion between the rollers and their mating surfaces has not been eliminated. No axial or pivoting movement of either the roller or its mating surface is provided to reduce the degree of sliding sustained. U.S. Pat. No. 4,490,126 provides pivoting action of the planar surface. However, the pivoting of the planar itself induces a frictional drag that reduces the efficiency of the CV joint.
Another disadvantage to the Orain triplan joints is the limitation of the joint's plunge--the extent to which the drive and driven shafts can be angulated. The plunge of the disclosed triplan joints is limited by the length of the needle roller assembly. Once the planar surface has traversed the quantity of needles provided, the remainder of any required plunge will be limited to sliding of the planar surface upon the needles. Consequently, the efficiency of the CV joint is markedly reduced.
As can be seen from the above discussion, the prior art does not teach a tripod CV joint which simultaneously minimizes the periodic sliding action between the roller member and it mating surface while also avoiding the asymmetrical rolling-sliding condition. This common shortcoming of the prior art results in a reduced efficiency of the CV joint. Where one reference attempts to avoid the periodic sliding action by providing a slidable and pivotal rolling member, its efficiency is reduced by an additional asymmetrical sliding action on the opposing side of the rolling member. And where another reference attempts to avoid both the periodic and asymmetrical sliding action by providing a mating surface that pivots with the rolling member, its efficiency is still limited by the drag resulting from the pivot action of the mating surface.
Accordingly, what is needed is a tripod CV joint with the advantages of having a roller member that is both slidable with and rotatable about is corresponding trunnion in order to maintain the roller's plane of rotation parallel to the guideways, while also avoiding the asymmetrical sliding action between the roller member and its opposing mating surfaces. It would be additionally desirable to provide a tripod CV joint which can accommodate a high degree of angulation between the drive and driven shafts by providing for maximized plunge between the inner and outer joint members.